This invention concerns a viscosity sensor, and a device comprising the viscosity sensor, in particular but not limited to a device for continuously controlling a quenching bath.
In a large number of applications, an industrial part needs to undergo a quenching operation after a thermic treatment to obtain the mechanical properties required for proper operation of the industrial part. Such a quenching operation can take place in various media including water, oil, dissolved salt and a water-polymer mixture.
In a typical quenching operation, the parts are first heated to a high temperature (e.g., about 900xc2x0 C.). The heated parts are then cooled, down to an ambient temperature, by following a controlled cooling rate which depends on the type of fluid used for the quenching.
The power supplied to the quenching bath is called xe2x80x9cdrasticityxe2x80x9d. For quenching baths that use water, salt or oil, drasticity is ordinarily fixed, and specified by the supplier.
Polymers have the advantages that they are non-flammable, non-polluting, non-toxic, and that they are able to be washed with water. For water-polymer mixtures, drasticity depends on the type of polymers used, the concentration of the mixture, and aging of the mixture. During successive quenchings, the polymer bath loses its properties due to product aging, water evaporation, removal of the polymer from the bath by adherence to the parts, thermic effects, and the presence of metal particles and soot in the bath. For these reasons, the user must regularly monitor the quality of the polymer bath to keep the bath at its correct drasticity value.
Drasticity is presently controlled either by direct measurement of the drasticity or by indirect measurement.
Drasticity can be directly measured using a drasticimeter, a device which is capable of measuring the cooling curve of a silver-calibrated test piece immersed in a bath having known characteristics, volume and agitation. The use of a drasticimeter is the only known method which gives a true measurement of drasticity. However, this requires the use of complex equipment which is generally reserved for laboratories.
For the indirect measurement of drasticity, a parameter representing the highest possible degree of drasticity, such as refraction index or viscosity, can be measured by various means. Refraction index can be measured manually, using a refractometer, permitting rapid measurement which can be carried out in a workshop for determining the polymer concentration of the quenching bath. While this is an effective measurement, such measurements can be carried out only for a new bath. Viscosity can be measured using a viscosimeter. While this results in a more precise measurement than a manual measurement with a refractometer, viscosity measurements are exclusively carried out in the laboratory.
Consequently, the two types of indirect measurement currently used cannot be continuously effected in the quenching bath, but are instead made on samples taken from the bath.
The Hardening Fluids Commission of the A.T.T.T. (Technical Association for Thermic Treatment) recommends viscosity as the element to be monitored for purposes of monitoring aging of the polymer. Reading the refraction index is not considered very precise because it is sensitive to all types of pollution. Measurement using a Utbelhode tube is recommended, and a standard to this effect has been published (see, article-extracts of the A.T.T.xe2x80x94Lyonsxe2x80x94June 1997).
To facilitate control and maintenance of the quenching bath, users need to have, in situ, a continuous measuring system for regulating the quality of the bath. However, no method for the continuous control of the drasticity or viscosity of a quenching bath is currently known (see, Quenching filexe2x80x94Thermic Treatment Journalxe2x80x941997). Viscosimeters that can operate continuously are used in other fields of application, such as for foodstuffs, resins, paints and other materials, but none is adaptable to the field of thermic treatment or sufficiently sensitive to provide the required values and precision.
The object of the present invention is to develop a viscosity sensor and a measurement device that can satisfy the specific needs for continuously controlling polymer baths used for quenching parts and that is strong enough to withstand the working conditions in forges and smelting works, that exhibits no drift or wear, that functions with a simple energy element, and that is insensitive to external disturbances. In addition, the sensor and the device must be able to calculate and continuously regulate the polymer concentration of the quenching bath.
These and other objects can be achieved by resolving the large number of difficulties faced in implementing such equipment, especially concerning the accuracy of guidance.
Such objects can be achieved with a viscosity sensor that operates on a principle of measurement that is based on the time taken by a piston centered in a measuring chamber of a calibrated tube immersed in a liquid bath to fall. The sensor is generally comprised of a lifting element that lifts up from a predetermined height in a mobile unit that includes the piston and at least one unit for transmitting movements of the piston. The mobile unit further includes a detection element, at its upper portion, which is primarily formed of a tubular body fixed to a rod associated with the transmitting unit, for example, at the center of a disk enclosing the tubular body. The detection element slides longitudinally inside a generally cylindrical measuring sensor which carries at least one detector for detecting movement of the detection element, and is lifted up by the lifting element using a finger which is fixed radially on the detection element and which traverses a longitudinal slit in the measuring sensor body.
Also provided is a device comprising the viscosity sensor and an electronic regulator that receives the information sent by the detector and that, through calculation, deduces the viscosity of the fluid. The device can further include a temperature detector so that the electronic regulator can calculate an equivalent viscosity which is brought down to a reference temperature, The electronic regulator is preferably able to calculate (by deduction) the concentration of a water/polymer mixture, depending on the type of polymer used, and to act on valves associated with the device to regulate and readjust the concentration of the bath according to the results obtained.
In the description which follows, such a device is referred to as a xe2x80x9cdrasticimeterxe2x80x9d, the structure of which will be more readily understood from the description which follows, with reference to the accompanying figures.